Morphology-controlled Preparation Of The Supported Br?nsted Acid Catalysts And Their Performance In Biomass Conversion

Catalytic conversion of the renewable,inexpensive biomass resources and their derived platform compounds into high-quality biofuels and high value-added organic chemicals can effectively reduce dependence on depleted fossil fuels and reduce emissions of pollutants and greenhouse gases.From the point of green chemistry and sustainable technology,the development of high-efficient and recyclable environment-friendly catalysts and the study of their performance in low-cost biomass conversion are the central scientific issues of this reaearch.Solid acids are important catalysts for biomass conversion,and they can be used in biomass conversion process with a broad applications by overcoming the disadvantages of reaction equipment corrosion and environmental pollution caused by homogeneous acids such as H2SO4 and p-toluenesulfonic acid.However,the reported commercial or traditional solid acid catalysts are not enough to satisfy the practical applications owing to their low catalytic activity and poor stability.In order to solve the above problems,this doctoral dissertation devoted to the morphology-controlled preparation of novel,efficient and recyclable supported Br?nsted acid catalysts,including hierarchically porous nitrogen-doped carbons supported Br?nsted acidic ionic liquids,organosilica nanotubes supported sulfonic acids and organosilica hollow nanospheres supported Br?nsted acidic ionic liquids.Meanwhile,the catalytic activity,selectivity,reusability and reaction mechanism of the prepared supported Br?nsted acid catalysts were studied.The key points of this paper focused on: i)the Br?nsted acid sites were introduced into the nitrogen-doped carbon or organosilica supports by chemical bonding so that the uniform dispersion of the acid sites were obtained;meanwhile,leakage of the acid sites into the reaction media can be inhibited effectively;ii)the activity and selectivity of the supported acid catalysts were further improved by well-controlled morphology,porosity properties and surface hydrophilicity;and iii)the performance of the prepared supported acid catalysts in biomass conversion were systematically evaluated by the reactions including crude pyrolysis biofuel upgrading,biodiesel synthesis,esterification of glycerol with laurate acid and dehydration or alcohololysis of fructose.The specific contents are as follows.1.Hierarchically porous nitrogen-doped carbons(NHPCs)with interesting 3D interconnected macro-meso-microporous structure were successfully obtained via a single step Ca CO3 nanoparticle-directed nanocasting approach combined with K2C2O4 chemical activation during the process of carbonization of glucose and urea/melamine.Subsequently,through quaternary amination with 1,3-propyl sulfonolactone and anion exchange with HSO3CF3,a series of nitrogen-doped carbon supported Br?nsted acidic ionic liquids(GU/GM? [C3N][SO3CF3],C3 = Pr SO3H)were successfully prepared.The composition,structure,morphology and porosity properties of the catalysts were studied in detail by various characterization methods.Moreover,the formation mechanism of the hierarchically porous structure of the GU/GM? [C3N][SO3CF3] was discussed.The heterogeneous acid catalytic properties of the GU/GM? [C3N][SO3CF3] were systematically studied in the esterification of acetic acid with high boiling point benzyl alcohol or 4-methoxybenzyl alcohol,which is one of the effective strategies to decrease oxygen content and acidity of raw pyrolysis biofuels;meanwhile,the produced esters are value-added compounds.The GU/GM? [C3N][SO3CF3] catalysts exhibit considerably high esterification activity,attributed to the synergistic effect of macro-meso-micropores within the catalysts and super strong Br?nsted acidity,which can significantly improve the accessibility of the reactants to the acid sites via minimizing the diffusion resistance,shortening mass transport pathway and increasing acid site population.Moreover,the esterification activity of the GU/GM? [C3N][SO3CF3] catalysts is dominated by their macroporosity properties.More importantly,owing to chemical bonding Br?nsted acidic ionic liquid throughout the NHPC supports,the GU? [C3N][SO3CF3] can be reused for five times without remarkable activity loss and morphology change,and they are genuinely heterogeneous catalysts and display high catalytic stability and recycling performance.2.One-step toluene-swollen mixed Pluronic surfactant(P123 and F127)micelle-templating sol-gel strategy combined with hydrothermal technique was designed to prepare a series of organosilica nanotubes supported sulfonic acids(Ar/Pr SO3H–Si(Et)Si)successfully via co-hydrolysis and-condensation of both 1,2-bis(trimethoxysilyl)ethane and(3-mercaptopropyl)trimethoxysilane/2-(4-chlorosulphonylphenyl)ethyltrimethoxysilane in a strong acid media by carefully controlling composition ratio of bridged organosilanes to the copolymer surfactants.The inner diameters and lengths of the Ar/Pr SO3H–Si(Et)Si nanotubes can be easily adjusted in a wide range by changing the swelling agent concentrations.The composition,structure,morphology and porosity properties of the catalysts were studied in detail by various characterization methods.Moreover,the formation mechanism of the Ar/Pr SO3H–Si(Et)Si nanotubes was discussed.The heterogeneous catalytic performance of the Ar/Pr SO3H–Si(Et)Si nanotubes were systematically evaluated in transesterification of tripalmitate with methanol to methyl palmitate and selective esterification of glycerol with lauric acid to glycerol monolaurate and glycerol dilaurate.Ar/Pr SO3H–Si(Et)Si nanotube catalysts exhibited extremely high transesterification and esterification activity,which strongly depend on their Br?nsted acid nature;additionally,inner diameter,length and BET surface area of the nanotube catalysts influence the activity in some extent by facilitating the diffusion and mass transport of thereactants/products as well as improving the accessibility to the acid sites;finally,the surface hydrophobicity of the Ar/Pr SO3H–Si(Et)Si nanotubes can boost the formation of FAMEs and glycerol laurate esters through changing the adsorption/desorption behaviors of the reactants/products.Moreover,the Ar/Pr SO3H–Si(Et)Si catalysts showed excellent catalytic activity in biodiesel production from various plant oils including rapeseed oil,sunflower oil and yellowhorn seed oil.The Ar/Pr SO3H–Si(Et)Si nanotubes also exhibit excellent catalytic reusability and stability,and the changes of activity loss,structure,morphology,acidity and porosity properties are hardly observed after five consecutive cycles,attributing to the covalent bonding of the Ar/Pr SO3 H groups within the silica/carbon framework.3.One-step toluene-swollen F127 surfactant micelle-templating sol-gel strategy combined with hydrothermal technique was designed to prepared chloropropyl functionalized organosilicon supports with hollow nanospheric morphology(Pr Cl–Si(Et)Si)via co-hydrolysis and-condensation of both 1,2-bis(trimethoxysilyl)ethane and3-chloropropyltrimethoxysilane in a strong acid media.The inner diameter(5–14 nm)and shell thickness(5–9 nm)of the supports were adjusted by changing the concentrations of swelling agent toluene.Afterwards,a series of organosilica hollow nanosphere supported Br?nsted acidic ionic liquids([C3/4Im][OTs/OTf]-Si(Et)Si,C3 = Pr SO3 H,C4 = Bu SO3 H,[OTs]= p-CH3C6H4SO3,[OTf] = CF3SO3)with different inner diameter(5–14 nm)and shell thickness(5–9 nm)were successfully prepared by decorating Pr Cl–Si(Et)Si with imidazole,1,3-propyl sulfonolactone(or 1,4-butane sulfonolactone)and HSO3CF3(or p-toluenesulfonic acid)successively.By changing the carbon-chain lengthes of cations and anionic structures of ionic liquids,the surface hydrophobicity and Br?nsted acid strength of the catalysts can be regulated,respectively.The composition,structure,morphology and porosity properties of the catalysts were studied in detail by various testing methods,and the formation mechanism of the hollow nanospheric morphology was therefore discussed on the basis of the above results.The heterogeneous acid catalytic properties of as-prepared [C3/4Im][OTs/OTf]-Si(Et)Si were systematically evaluated in microwave-assisted fructose dehydration to5-hydroxymethylfurfural(5-HMF)and alcoholysis to 5-ethoxymethylfurfural(5-EMF),respectively.Compared with the traditional heating method of high pressure reactor,it is found that microwave irradiation plays an important role in increasing the reaction rate and the selectivity of products of to the target reactions.With the synergistic effect of microwave heating and catalysis of the [C3/4Im][OTs/OTf]-Si(Et)Si,the target products with high yield were obtained in a very short time.For the fructose dehydration reaction,the surface hydrophobicity of the catalysts plays the dominated role in generation of 5-HMF.As for the fructose alcohololysis reaction,the Br?nsted acid strength of the catalysts plays a key role in the synthesis of 5-EMF.In addition,the prepared catalysts have a good recycling performancein both model reactions,originating from the covalently bonding interaction between the acidic ionic liquid and imidazole functionalized silicon/carbon framework.The present work therefore provides new strategies to fabricate carbon or silicon supported Br?nsted acid catalysts;meanwhile,their catalytic performance in conversion of biomass or biomass-derived platform compounds into biodiesel and important chemicals was systematically evaluated.The relationship between the Br?nsted acidity,morphology,surface hydrophobicity and porosity properties of the catalysts with their reactivity and selectivity was revealed.Moreover,the reaction mechanisms were put forward.In consequence,this work can provide some references for catalytic conversion of biomass resources to biofuel and chemicals over the supported Br?nsted acid catalysts.